Noncontact infrared temperature sensors absorb ambient infrared (IR) radiation emitted by a heated surface. They are used in a variety of applications where direct temperature measurement is not possible. With noncontact infrared temperature sensors, incoming light is converted to an electric signal that corresponds to a particular temperature. Although many different types of products are available, noncontact infrared temperature sensors can be thought of as belonging to general categories based on design and application. This category criteria attempts to distinguish unpacked devices that can be used as part of a larger sensor from, say, a gauge which can be read by simple examination. Categories for noncontact infrared temperature sensors include sensor elements or chips, sensors or transducers, gauges or indicators, and instruments or meters.
 
Operating specifications for noncontact infrared temperature sensors include technology type and electrical outputs. Common technologies include thermal-based bolometers, thermocouples or thermopiles, pyrometers or pyroelectric devices, and optical pyrometers.  Electrical output options for noncontact infrared temperature sensors include analog current, analog voltage, analog frequency, serial, parallel, other digital, and switch or alarm. Additional operating specifications to consider when selecting noncontact infrared temperature sensors include accuracy, which is specified as a percent or in degrees; and repeatability, which is specified normally as a percentage. Target emissivity, response time, and the ratio of the distance to the target or spot-size are additional considerations.